1. Field of the Invention
The subject invention relates generally to voltage multiplying circuits and, more particularly, to DC-to-DC voltage multipliers of the type wherein an energy-storing coil is alternately connected across a DC voltage source and, in series with the voltage source, across a storage capacitor.
2. Description of the Prior Art
Portable electronic equipment almost universally employs battery powered transistor circuits. Most such circuits require for their operation a supply voltage level higher than that produced by a conventional battery cell whose output toward the end of its life can drop to as low as 0.9 volts. Consequently, several battery cells must usually be connected in series to operate such transistor circuits, resulting in increased complexity and, hence, cost.
Circuits are available for converting a poorly regulated, low level DC voltage to a closely regulated DC voltage at a higher level, a process called "DC-to-DC up-conversion". Such circuits are limited by the voltages at which they can operate. None are known to operate from a single battery cell, particularly not when the output voltage of that cell has dropped due to use or age, or both, to a level significantly below 1.5 volts.
One type of circuit used for DC-to-DC up-conversion includes a coil which is alternately connected by means of an electronic control circuit across a source of DC potential and in series with that source across an output capacitor, thereby generating across the capacitor a voltage which, through a number of cycles, is built up to a higher level than that of the DC potential source. Such a voltage converter circuit usually includes a transistor switching circuit to make the alternate connection of the coil across the source of DC potential and to the output capacitor. In addition, the circuit includes a pulse width modulator for driving the switching circuit and an oscillator for driving the pulse width modulator. The control circuit operates by modulating the duty cycle of the pulse width modulator in response to the voltage across the output capacitor, thereby regulating the duration of the time periods during which the switched coil is connected to discharge its energy into the output capacitor. In this way, the voltage across the output capacitor can be maintained quite precisely.
A shortcoming of the above type of converter circuit is that its operating voltage is usually derived from the DC source whose level is to be stepped up through operation of the circuit. Since such circuits require, for their operation, a voltage which corresponds to the output of several battery cells connected in series, they cannot be used to step up the voltage of a single battery cell.
Accordingly, it is a principal object of the present invention to provide a circuit capable of converting the output of a single battery cell to a stable voltage at a level which is a multiple of the battery cell's output voltage.
A related object of the present invention is to provide a voltage regulating circuit capable of operating from extremely low voltage levels.
A more specific object of the present invention is to modify currently available voltage regulating up-converters so as to reduce the voltage they require for their operation.